1. Field of the Invention
This invention relates to magnetic recording mediums which are suitable for horizontal magnetization recording and which have a Cr undercoat layer and a magnetic Co alloy layer formed on the undercoat layer. The invention also relates to a method for making such mediums.
2. Description of the Prior Art
In recent years, those magnetic recording mediums for high density recording using a magnetic Co alloy film have been often employed. In particular, rigid or hard disks making use of a Cr undercoat layer and a magnetic Co alloy layer formed on the undercoat layer have been studied in order to increase the coercive force, Hc. To this end, a variety of elements have been added to the Cr undercoat layer. For instance, when elements such as Gd, Ce, Cu, Si, etc., are incorporated in the Cr undercoat layer in an amount of about 1 atomic percent, the coercive force is increased by about 100 to 200 Oe as compared with the case where no additive element is added. Over 1 atomic percent, the coercive force, Hc, tends to decrease
("Effects of Substituted Elements into the Cr Layer on CoNiCr/Cr Sputtered Hard Disk" in Reports of the 12th Meeting of the Japan Applied Magnetic Society).
However, the increase of the coercive force by approximately 100 to 200 Oe is not satisfactory for use as high density magnetic recording mediums. Moreover, it is very difficult to appropriately control the amount of the additive element at about 1 atomic percent.
Another type of high density magnetic recording medium of the horizontal magnetization type has been proposed wherein a Co alloy film or layer is incorporated with a certain amount of oxygen to improve magnetic characteristics and a corrosion resistance. For example, CoCr alloys are subjected to vapor deposition under an oxygen pressure of 1 to 3 mTorr., thereby forming an amorphous CoCr alloy film containing from 5 to 15 atomic percent of oxygen therein. This type of medium is described, for example, in Japanese Laid-open Patent Application Nos. 61-115244 and 61-105721 and U.S. Pat. No. 4,711,810. Moreover, a magnetic layer composed of Co, Ni and O with or without use of Cr is formed by oblique vapor deposition techniques while controlling the content of oxygen, thereby improving magnetic characteristics and a corrosion resistance (Japanese Laid-open Patent Application Nos. 59-58804 and 59-61105.
However, the CoCr alloy film is amorphous in nature and has thus no magnetic anisotropy, so that the maximum coercive force is in the range of from 500 to 600 Oe. This is not satisfactory for use as a medium for high density recording. In addition, the oblique vapor deposition is disadvantageous in that much of the starting material is consumed in vain.